Most commonly, metal sheets are fastened together using rivets or spot welds. These methods of fastening, however, have their drawbacks inasmuch as the spot welds leave a weld scale and burn the surface of the sheets. Spot welding is also not effective in sheet materials which are not easily welded, such as is the case with very thin or dissimilar materials. Furthermore, the burned sheets may leave an unacceptable aesthetic appearance. Rivets can perform a similar function but they do not leave a finish flush with the surface of the sheets which may be a requirement in some applications. As yet another alternative, adhesives or other bonding agents such as epoxies can be used, however these are often very messy and very costly. Additional methods such as Tog-L-Loc® which forms sheets together and Henrob style fasteners deform the sheets being attached. Allowing for rotation is also possible. Of the technologies discussed above, the additional feature of rotation can only be accomplished by a rivet which does not install flush.
U.S. Pat. No. 3,242,962 to Dupree discloses a double-sided clinch type insert which installs between the sheets being joined. However, there are many problems and disadvantages of the Dupree fastener. For example, it allows for installation of only one fastener, due to the fact that once the sheets are joined nothing additional can be inserted between them. This also negates the advantage of autofeeding and installing the Dupree fastener using more efficient, modern techniques. In addition, the Dupree fastener must be the same thickness as the width of the combined sheets. And finally, while the Dupree fastener may be modified to permit rotation by removing a knurl in one of the undercuts, the rotating clinch would significantly weaken and fail after numerous cycles.
There is therefore a need in the art for means for securing two metal sheets together which provides flush finish on both metal sheets, with the additional feature of providing a pivot for rotation, and avoids the weld scale or epoxy mess of the aforementioned fastening methods.